Two forms of adjuvant therapy designed to improve the effectiveness of I-131 radiation in thyroid cancer are under study. The first is lithium ion, which is used to prolong the retention of I-131 in the cancer. Preliminary findings have been described in previous annual reports. The second is the use of doxorubicin (adriamycin) as a radiosensitizing agent. To evaluate its effectiveness, we have begun a randomized study of high-risk thyroid cancer patients who receive standard I-131 therapy with or without the administration of low-dose adriamycin (10mg/square m) 30 min preceding each I-131 treatment dose. To our knowledge, this is the first attempt to randomize patients in a therapy protocol for thyroid cancer employing I-131. Other patients with negative I-131 whole body scans but elevated concentration of thyroglobulin in blood are given I-131 therapy in an attempt to localize the cancer by post-therapy scanning. Most patients have been found to have positive post-therapy scans and they are under evaluation for possible beneficial effects of the therapy.